1. Field of the Invention
This invention relates to sheaths and introducers, which are utilized in a human heart, which has been altered by heart disease. More particularly, this invention relates to a telescopic peel-away catheter with a core.
2. Description of the Prior Art
The coronary sinus is the largest cardiac vein and serves as a conduit for access to various locations within the heart. Depending on the depth of insertion of the medical device into the coronary sinus, both the left and right atria and the left and right ventricles of the heart can be analyzed. However, introduction of a medical device into the ostium of the coronary sinus is quite difficult as a result of the structure of the heart, the difficulty in locating the coronary sinus using conventional medical technology and the constantly changing shape of the heart while beating as well as the altered anatomy of the heart with cardiomyopathy.
The anatomy of the coronary sinus branch vein presents novel problems for canulation and pacemaker insertion. During pacemaker implantation the delivery system must be steerable to properly locate and insert itself into the ostium of the coronary sinus. Thereafter, the delivery device must have the ability to be steered through a highly branched vasculature to smaller and smaller vessels, yet it must not be so stiff or biased to be traumatic to the vessels. After implantation the delivery system must then leave in place a highly flexible, poorly steerable pacemaker lead.
Two approaches are commonly used for placement of a medical device within the coronary sinus, an inferior approach from below the heart, and a superior approach from above the heart. In the superior approach, the device is advanced through either the right or left cephalic or right or left subclavian vein through the superior vena cava into the right atrium until it is directed toward the coronary sinus. See FIG. 1a. In the inferior approach, the device is generally advanced through the femoral vein through the inferior vena cava into the right atrium. See FIG. 1b. The tip of the device is then directed toward the ostium of the coronary sinus. The superior approach is the preferred approach and is the approach for which the introducer of the present invention is optimized.
Telescopic catheters are well known and applied to a variety of arterial operations, but never before into the venous system. Typically, one use for such catheters is in the placement of angioplasty balloons in heart arteries. The following United States patents disclosed various forms of dilatation catheters: U.S. Pat. Nos. 3,435,426; 4,271,839; 4,323,071 and 4,338,942. The use of a guiding catheter having a distal tip that can be shaped to facilitate positioning or guiding a catheter into a selected coronary blood vessel is thus well known. Successful angioplasty requires that the balloon of a dilatation catheter be positioned within a stenosis. The more severe the stenosis, the more pressure required to position the dilatation catheter within it. Although very few stenoses within the main coronary artery are so severe as to be impenetrable by a balloon catheter, about 30% of stenoses located in the left circumflex artery cannot be treated with angioplasty. Such is the case because transmission of axial force to the distal end of the catheter from the proximal end is impeded by presence of a sharp bend where the catheter shaft traverses the intersection of the circumflex artery with the main artery.
Thus telescopic catheters have been devised as shown in U.S. Pat. No. 4,616,652 for introducing guide for a balloon catheter. The guide is composed of three parts that are relatively axially movable in telescoping relation to one another. The inner-most part is formed of wire the distal end of which can be selectively deformed to facilitate the manipulation of the distal end through blood vessel intersections. The center or intermediate part, which has a central lumen in which the wire is telescoped, has a tapered distal end and is formed of material possessing sufficient rigidity to be advanced along the wire after the wire is in place, and sufficient flexibility to conform to the wire configuration. The outer part telescopes on to the exterior of the intermediate part. The outer part defines a passage having an inside diameter that is large enough to afford entry of a balloon catheter therethrough. The outside diameter of the intermediate part is less than the inside diameter of the passage so that when the wire and intermediate part are positioned, the outer tube can be advanced therealong.
Thus the telescopic introducer for a dilatation catheter has sufficient flexibility to be manipulated around irregular paths, such as occur within the intersection between the main artery and the left circumflex artery, but has sufficient stiffness or rigidity that it can be moved to a position adjacent a stenosis to be treated by angioplasty. This object is effected by providing an introducer composed of three relatively axially movable parts which are so arranged that the clinician can individually control the relative axial position of each of the parts. The guide wire contained within the innermost guide controls the direction of the intermediate telescoping introducer. The introducers by themselves are not capable of negotiating the branch vessels of the coronary arteries, but instead rely on the navigation of the wire to control the direction for subsequent guides to follow.
Generally in the arterial system shaped sheaths are not used to navigate the branches of the coronary arterial system, but sheaths and catheters are generally placed using a guidewire. The reason for this is that in the high pressure arterial system there is a high probability of the existence of plaque on the artery walls. Any undue disturbance risks the dislodgment of that plaque with the possibility of a resulting heart attack or stroke. However, in the low pressure venous system plaque is not present and the interior vessel walls are smooth. Thus, while a guidewire can also be used in the venous system, the use of shaped sheaths, introducers and catheters which can be steered without a guide wire is safe. To be steered such shaped sheaths, introducers and catheters must be torqueable or rotatable from their proximal end. It is desirable then to have both a radially flexible sheath, introducer and catheter to avoid trauma to the vessel walls and to more easily track in a tortuous or highly branched venous system, while at the same time to be shaped and torqueable. Generally, to be torqueable and radially flexible at the same time meant that the sheath, introducer and catheter had to include a braided reinforcement in or on it. However, a braided sheath, introducer and catheter means greater expense in fabrication of the sheath, introducer and catheter as well as a larger diameter of the sheath, introducer and catheter or a smaller inner diameter of any lumen in the sheath, introducer or catheter.
One prior art approach has been that shown in U.S. Pat. No. 6,185,449 in which a braidless catheter is combined with a solid inner guide 60. While the catheter is thus not torqueable, the inner guide 60 is inserted in a lumen defined within the catheter and the inner guide 60 is torsionally stiff enough to be torqueable. The catheter is hopefully rotated when the inner guide 60 is rotated. However, in this prior art case the inner guide 60 is rendered torqueable simply by having a sufficiently large enough diameter that it is rendered torsionally stiff given the material from which it is made. Since the material is of a uniform extrusion, the flexural characteristics of the core are uniformly soft or rigid. There is nothing in the structure of inner guide 60 which renders it torsionally stiff or imparts to it the necessary varied characteristics of torque versus flexibility needed for steering coronary sinus venous catheters. Such a limitation of the diameter of inner guide 60, then limits the size of the catheters with which it is used to those having larger diameters and particularly larger diameter lumens in them to accept the larger diameter inner guide 60.
Venous coronary sinus procedures or pacemaker implantations, however, require not a distal stiffness to push through a stenosis, but a variable and controllable distal flexibility or softness, torque control as well as specific distal curves. Therefore, some means is needed to adapt telescoping guides or introducers to achieve this different and opposite object from those realized by arterial telescopic introducers.